A secret's a hard thing to keep in the gaming world. nVidia had planned to introduce its next-generation graphics chip Feb. 5 at a swanky affair in San Francisco. All questions about the chip were brushed aside with a knowing wink that said "wait and see." As PR strategies go, it was a pretty smart one, creating interest and building curiosity. Then the Power Mac G4 happened. Apple's newest, most powerful machine has just gone on sale at Apple.com. Look close at the included components, though, and listed among them is a video card featuring the GeForce 4. The chip, which is the company's successor to the GeForce 3 (a kissing cousin of the chip that's used to power Microsoft's Xbox), takes over several of the calculations formerly performed by a computer's CPU, allowing the machine to focus more on game speed and resulting in graphics that look more realistic than ever. Assuming developers code their games right, you'll see better collision detection (in other words, if you're playing the latest "Madden" game, you won't see one character reach through the body of another when making a tackle) and smoother movement in character joints (allowing your on-screen persona to move more like a live person does).